System and method for 3-d imaging

ABSTRACT

A system and method for recording and depicting ultrasound images of a moving object are disclosed. In a preferred embodiment, ultrasound images are acquired as the field of view of an ultrasound probe is advanced across the tissues of interest during a resting period between periods of relatively large-scale heart cycle motion. A series of images acquired during a particular resting period may be represented as a three-dimensional volume image, and the comparison of volume images from adjacent cardiac resting periods enables three-dimensional volume image modulation analysis which may be presented for a user as a moving volume image of the objects of interest within the field of view.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.10/923,660, filed on Aug. 20, 2004 which claims priority to U.S.Provisional Patent Application Nos. 60/496,944 filed Aug. 20, 2003 and60/506,231 filed Sep. 25, 2003 which the contents of which areincorporated herein by reference in their entirety.

BACKGROUND OF THE INVENTION

Imaging moving structures such as cardiac tissue walls and nearbymedical instrumentation presents a unique set of problems not ideallyaddressed in three dimensions by conventional devices employing imagingmodalities such as magnetic resonance imaging (“MRI”), computedtomography (“CT”), and ultrasound. One the challenges with MRI and CTimaging modalities is related to the requisite sampling rate useful formonitoring three dimensional motion of tissues moving with relativelyhigh frequency and high amplitude motion, such as cardiac tissues.Sophisticated arrays of ultrasound transducers, available in productsfrom suppliers such as Koninklijke Philips Electronics N.V., may beutilized to produce real-time three-dimensional visualization ofrelatively high-frequency, high-amplitude moving tissues such as cardiactissues, but such devices are generally large in size and configured fortransthoracic access to such tissues.

Maintaining transthoracic or similar contact and access during aprocedure involving the heart below or other similarly situated tissueof the body is difficult if not impossible, depending upon theparticular procedure. Smaller ultrasound systems have been designed andutilized for catheter-based deployment to provide more direct access forimaging tissues and providing instrument guidance feedback. Productssuch as the side-firing ultrasound catheter sold by Siemens Corporationunder the tradename “AcuNav™” the diagnostic ultrasound catheters soldby EP-Technologies-Boston-Scientific Corporation under the tradename“Ultra ICE™”, or the intravascular ultrasound imaging catheters sold byJomed Corporation under the tradename “Avanar™”, for example, may becombined with software and automated position advancement technologyfrom suppliers such as Tom Tec Imaging Systems GmbH of Munich, Germany,to produce three-dimensional renderings of various tissue structures ofthe body, such as vascular and cardiac tissue structures fromendovascular and endocardial perspectives. The ultrasound transducerhardware comprising such systems generally is fairly simple due to sizeconstraints, and this simplicity is advantageous for device complexity,cost, and disposability reasons. Use of these conventional systems toproduce three-dimensional renderings, however, generally requireshybridizing or “gluing together” datasets captured over relatively longperiods of time employing assumptions of tissue motion cycle homogeneityto produce three-dimensional renderings.

In medical fields such as remotely actuated or minimally invasivesurgery, it is desirable to have accurate, timely information regardingthe relative positioning of remotely deployed medical devices and nearbytissue structures such as tissue walls. For example, one may want tobiopsy a portion of a tissue wall with a mechanical end effector, injectsomething into and not beyond a tissue wall, or touch a tissue wall withan electrode, and have some confirmation, preferably inthree-dimensions, of the relative positioning between pertinent objectsduring such procedures. There remains a need for a means to producetimely three-dimensional relative positioning data utilizing anoninvasive modality such as ultrasound via relatively simple structuresand techniques.

FILED OF INVENTION

The present invention relates generally to ultrasound imaging systemsand, more particularly, to ultrasound imaging systems acquiringtwo-dimensional ultrasound images of a heart for display in athree-dimensional orientation.

BRIEF DESCRIPTION OF THE DRAWINGS

Preferred embodiments and other aspects of the present invention areillustrated in the figures of the accompanying drawings, in which likereferences indicate similar elements. Features shown in the drawings arenot intended to be drawn to scale, nor are they intended to be shown inprecise positional relationship.

FIG. 1 depicts an electrocardiogram plot of voltage versus time for atypical human heart.

FIG. 2A depicts various aspects of a conventional technique for creatinga three-dimensional image of a subject tissue mass and/or medicalinstrument.

FIG. 2B depicts an electrocardiogram associated with the imagingtechnique illustrated in FIG. 2A.

FIG. 2C depicts various aspects of a conventional technique for creatinga three-dimensional image of a subject tissue mass and/or medicalinstrument.

FIG. 3A depicts various aspects of one embodiment of the inventivetechnique for creating a three-dimensional image of a subject tissuemass and/or medical instrument.

FIG. 3B depicts an electrocardiogram associated with the imagingtechnique illustrated in FIG. 3A.

FIG. 3C depicts various aspects of one embodiment of the inventivetechnique for creating a three-dimensional image of a subject tissuemass and/or medical instrument.

FIG. 4A depicts various aspects of one embodiment of an imaging systemin accordance with the present invention.

FIG. 4B depicts various aspects of one embodiment of an imaging systemin accordance with the present invention.

FIG. 4C depicts various aspects of one embodiment of an imaging systemin accordance with the present invention.

FIG. 5A depicts a flow chart representation of a conventional imagingtechnique.

FIG. 5B depicts a flow chart representation of one embodiment of thepresent-invention.

FIG. 6A depicts a cross-sectional slice of subject tissue mass andmedical instrument represented without image distortion.

FIG. 6B depicts a cross-sectional slice of subject tissue mass andmedical instrument represented with image distortion.

FIG. 7A depicts a top view of field of view paths of subject tissue massand medical instrument wherein relatively large and relatively focusedfields of view are illustrated.

FIG. 7B depicts a side view of the objects and fields of view depictedin FIG. 7A.

FIG. 7C depicts a top view of field of view paths of subject tissue massand medical instrument wherein relatively large and relatively focusedfields of view are illustrated.

FIG. 7D depicts a side view of the objects and fields of view similar tothose depicted in FIG. 7C.

FIG. 8A depicts a top view of a relatively focused field of view pathcapturing aspects of a subject tissue mass and medical instrument.

FIG. 8B depicts a series of images that may be acquired utilizing thefield of view path illustrated in FIG. 8A.

FIG. 8C depicts a side view of an image acquired utilizing the field ofview path illustrated in FIG. 8A.

FIG. 8D depicts a top view of four sequential series of images, eachhaving four images capturing aspects of a field of view path similar tothat illustrated in FIG. 8A.

FIG. 8E depicts an image stack or image volume orientation of imagesacquired as illustrated, for example, in FIG. 8B.

FIG. 8F depicts four images in a series oriented as acquired, as in FIG.8B.

FIG. 8G depicts four sets of four images, each being oriented asacquired.

FIG. 8H depicts four sets of four images, each being reoriented into arectangular image stack.

FIG. 9A depicts four images in a series oriented as acquired with twoseparate but similar viewing perspectives.

FIG. 9B depicts four images in a series reoriented into a rectangularimage stack with two separate but similar viewing perspectives.

DETAILED DESCRIPTION OF THE INVENTION

In the following detailed description of embodiments of the invention,reference is made to the accompanying drawings in which like referencesindicate similar elements. The illustrative embodiments described hereinare disclosed in sufficient detail to enable those skilled in the art topractice the invention. The following detailed description is thereforenot provided, or otherwise to be taken, in a limiting sense, and thescope of the invention is defined only by the appended claims.

Referring to FIG. 1, an electrocardiogram (“EKG”) tracing for a humanheart is depicted. The two systolic heart cycles (122, 124) depicted areseparated in time by a resting period (110) of relatively low heartactivity, during the diastolic period of the heart cycle. Each of theactive systolic heart cycles (122, 124) in a healthy patient typicallycomprises a P-wave (100, 112), followed by a Q-wave (102, 114), then arelatively high amplitude R-wave (104, 116), an S-wave (106, 118), and aT-wave (108, 120) before returning to the relative inactivity during aresting period (110). As discussed above, conventional ultrasound-basedtechniques for three-dimensional visualization may involve compilingdatasets from several steps of acquiring images over time duringadjacent resting periods (110) and utilizing assumptions regarding themotion of objects within the pertinent field of view during such restingperiods. FIGS. 2A and 2B are useful in illustrating such convention.

Referring to FIG. 2A, a subject tissue mass (222) is positioned inactual three-dimensional space adjacent a medical instrument (224). Tovisualize the relative positioning of such objects, a side-firingultrasound instrument or catheter (220) may be positioned as shown,using conventional intravascular or intralumenal delivery techniques,for example, to capture, in a series of images, a target volume of thetissue mass (222) and medical instrument (224), or portions thereof,within the field of view (242) of the ultrasound transducer. Usingconventional techniques, the ultrasound field of view (242) may beoriented in a first position (228) and utilized to acquire a firstseries of images while in the first position (228), generally during aresting cycle between two systolic heart cycles, for example, in thecase of a heart tissue subject.

Referring to FIG. 2B, this first series of images may be acquired duringa first acquisition cycle (250) positioned between a first systolicheart cycle (200) and a second systolic heart cycle (202). The firstacquisition cycle (250) may be defined by a first acquisition start time(212), at which the first image in the first series is acquired, and achange in time (“ΔT”) during which the remainder of the images of thefirst series are acquired, as illustrated in FIG. 2B. For example,during the first acquisition cycle (250), four ultrasound images may beacquired with the transducer field of view in the first position (228).

Similarly, subsequent to the second systolic heart cycle (202) and arepositioning (226) of the transducer field of view (242) to a secondposition (230), a second series of images may be acquired during asecond acquisition cycle (252) defined by a second acquisition cyclestart time (214) and a “ΔT” (210) as illustrated. Further, subsequent tothe third systolic heart cycle (204) and a repositioning (226) of thetransducer field of view (242) to a third position (232), a third seriesof images may be acquired during a third acquisition cycle (254) definedby a third acquisition cycle start time (216) and a ΔT (210) asillustrated. Finally in this illustration, subsequent to the fourthsystolic heart cycle (206) and a repositioning (226) of the transducerfield of view (242) to a fourth position (234), a fourth series ofimages may be acquired during a fourth acquisition cycle (256) definedby a fourth acquisition cycle start time (218) and a ΔT (210) asillustrated. Such a pattern may be repeated past a fifth systolic heartcycle (208) as would be apparent to one skilled in the art. Theincremental repositioning of the transducer field of view (242) betweenpositions (228, 230, 232, 234) may be associated with substantiallyequivalent changes in rotational position (236, 238, 240) of thetransducer field of view (242), as illustrated in FIG. 2A.

The scenario described above in reference to FIGS. 2A and 2B representsa fairly good case scenario utilizing conventional hardware andtechniques, since many systems are incapable of repositioning betweenimmediately adjacent acquisition cycles, and instead must consume one ormore systolic heart cycles for repositioning in between systolic cyclesused for acquisition. For example, a typical conventional system mayacquire a series of images at the first position (228) during a firstsystolic cycle, then utilize the next immediately adjacent systoliccycle for repositioning to a second position (230), and resume acquiringwith the second acquisition cycle during a third systolic cycle, therebystretching out the process in time to an even greater degree thanillustrated in FIG. 2B.

Subsequent to such an image acquisition schema, data from each of theacquisition cycles (250, 252, 254, 256) may be complied into avolumetric representation of the imaged objects (222, 224) moving perthe modulation of four image “slices”, each of which is associated withone of the field of view positions (228, 230, 232, 234), over time. Forexample, to produce a visualization of the changes in relativepositioning of objects (222, 224) over a time period such as ΔT, a firstfour-image volumetric representation comprising a first image acquiredat T1 (212) and the first transducer field of view position (228), nextto a second image acquired at T2 (214) and the second transducer fieldof view position (230), next to a third image acquired at T3 (216) andthe third transducer field of view position (232), next to a fourthimage acquired at T4 (218), may be compared with a second four-imagevolumetric representation comprising a first image acquired at T1(212)+ΔT (210) and the first transducer field of view position (228),next to a second image acquired at T2 (214)+ΔT (210) and the secondtransducer field of view position (230), next to a third image acquiredat T3 (216)+ΔT (210) and the third transducer field of view position(232), next to a fourth image acquired at T4 (218)+ΔT (210). The terms“volumetric image”, “volumetric representation”, and “image volume” areall used in reference to conventional techniques commonly used inmedical imaging, for example, wherein a series of images acquired atdifferent positions along or about a target volume are positionedadjacently within a graphical display interface, in spatial orientationsrelative to each other and the acquiring device similar to those duringacquisition, to facilitate representation of the state of the object inthree-dimensional format. One such schema is illustrated in FIG. 2C.Referring to FIG. 2C, a first image volume (800) assembled from fourheart cycles is compared (808) with a second image volume (802), alsoassembled from four heart cycles in this example, to provide aconventional three-dimensional visualization schema which may bedisplayed offline in simulated real-time. With such a technique, each ofthe image volumes (800, 802) is utilized like a depiction of the stateof the pertinent three dimensional objects at a given time, and changesin the image volume may be interpreted as changes in the relativepositions of objects within the image volume over time.

One of the key challenges with such conventional schemas is accuratelyand repeatably gating the acquisition cycle start times T1 (212), T2(214), T3 (216), and T4 (218) with the systolic heart cycle (200, 202,204, 206, 208) activity. Errors are introduced into such schemas as theresult of gating errors, heart cycle irregularities, and other cycles ormovements, such as breathing cycles, which may not be gated with theheart cycle. As would be apparent to one skilled in the art, “gluingtogether” an image volume from four different heart cycles forcomparison with another image volume for three-dimensional objectrelative position visualization inherently involves assumptions anderror—and also fails to accurately represent the state of the imagevolume together at any given time period for visualization purposes. Inother words, it is preferable to sequentially compare image volumescomprising individual images actually acquired in sequence—to accuratelyrepresent change within a given image volume over time. Conventionalsystems such as those described above essentially produce athree-dimensional dataset by gluing together images acquired atdifferent times, then replay a simulated three-dimensional motion imagein an offline format which is of relatively low utility as pertains toreal-time device guidance or positional monitoring.

Referring to FIGS. 3A-3C, the inventive system and technique improveupon the inherent problems with conventional techniques throughsequential image acquisition and repositioning, preferably within thesame resting period or adjacent resting periods, of the subject objectswithin a selected target volume. Referring to FIG. 3A, an embodimentanalogous to that illustrated in FIG. 2A is depicted, with the exceptionthat the embodiment of FIG. 3A is configured to change field of viewposition between, and in other embodiments during, acquisition ofsuccessive images. In one embodiment, for example, subsequent toacquisition of a first image at a first field of view position (228) ofan ultrasound transducer coupled to a medical device instrumentstructure (220) such as a catheter, the field of view (242) is rotated(302) from a first field of view position (228) to a second field ofview position (230), before acquisition of the next image. Such apattern is continued with images being acquired in between repositioningmovements to a third field of view position (232) and a fourth field ofview position (2.34). In one embodiment, the change in rotationalorientation of the transducer between each acquisition position ismaintained at a substantially constant angular rotation value. In apreferred embodiment, as illustrated in FIG. 3B, four successive imagesare acquired at four field of view positions (228, 230, 232, 234) duringmultiple successive resting periods between systolic heart cycles (200,202, 204, 206, 208). In one embodiment, it is desirable to acquireduring four or more immediately successive or adjacent systolic heartcycles to facilitate observing the motion of the pertinent structures inreal or near-real time on an imaging display.

Referring to FIG. 4A, one embodiment of a system for gathering,processing, and displaying three-dimensional images as described hereinis depicted. In the depicted embodiment, a target volume (14)encompassing portions of two tissue walls (10, 12) and a medicalinstrument (224) is selected by positioning an ultrasound transducer(16) at the end of an elongate flexible member (20), such as a roughlycylindrical member or catheter, so the field of view (242) of thetransducer (16) may capture the pertinent structures of interest as theelongate flexible member (20) is rotated (302). In the depictedembodiment, the elongate flexible member (20) preferably is delivered orpositioned into the body (18) through an existing lumen, such as agastrointestinal lumen, endovascular lumen, or endocardial space, forexample. Ultrasound catheters have been found useful for observingtissues such as endovascular walls and endocardial walls, in part due tothe access provided by catheter-based structures. In the depictedembodiment, the elongate flexible member (20) couples the ultrasoundtransducer (16) to a drive mechanism (24) configured to controllablyreposition the ultrasound transducer (16) through rotational drive. Thedrive mechanism (24) preferably comprises an electric motor of thestepper or linear format, such as those known to those in the art andavailable from suppliers such as MicroMo Electronics, Inc. and MaxonPrecision Motor, Inc. The drive mechanism (24) may also comprise agearbox, depending upon the physical demands upon the motor, and apositional encoder, such as those available from Hewlett PackardCompany, for monitoring rotational positioning of the attached elongateflexible member (20) as it is rotated (302) by the drive mechanism (24).Drive systems comprising gearboxes, motors, encoders, and couplingstructures configured to interface with flexible members (20) such asthe ultrasound catheter sold under the tradename AcuNav™ by SiemensCorporation are available from producers such as TomTec Imaging SystemsGmbH of Germany. To prevent windup or binding of transmission lines (22)within the elongate flexible member (20) as they interface with thedrive mechanism (24), conventional commutator interfaces (not shown) maybe utilized, as would be apparent to one skilled in the art. Due topotential signal degeneration and noise problems associated withcommutator type interfaces, in embodiments wherein the elongate flexiblemember (20) is repositioned before experiencing more than about 2 or 3complete revolutions, direct leads are maintained and configured withenough slack to permit such levels of windup without functionaldegradation.

In the depicted embodiment, a processor (26), preferably comprising anintegrated computer system, is in communication (22) with the ultrasoundtransducer (16) to receive and manipulate images acquired by theultrasound transducer (16), and deliver the images to a display system(28), such as a conventional computer monitor. In one embodiment havingrelatively elementary controls, the drive mechanism (24) may be operatedusing manual controls separate from the processor (26), and theprocessor (26) may be configured merely to receive data signals from theultrasound transducer (16) for displaying images with the display system(28). In other embodiments, the interaction between the processor (26)and drive mechanism preferably is more complex, utilizing conventionalsoftware-based device interaction techniques.

Referring to FIG. 4B, for example, an embodiment similar to that of FIG.4A is depicted wherein the drive mechanism (24), ultrasound transducer(16), and processor (26) have a feedback and control interaction. Theembodiment depicted in FIG. 4B also comprises a biological signal sensor(32), such as an EKG sensor, which is in communication (30) with theprocessor (26) to facilitate image processing and drive mechanismcontrol as related to an incoming biological signal. As would beapparent to one skilled in the art, having the system configured whereinthe processor (26) receives (34) encoder data from the drive mechanism(24), receives (22) transducer data from the ultrasound transducer (16),receives (30) biological signal data from a biological signal sensor(32), sends (34) position actuation signals to the drive mechanism (24),and sends image data to a display system (28) facilitates capture,processing, and display of data as described, for example, in referenceto FIGS. 3A-3C.

Referring to FIG. 4B, in another embodiment, a preferred systemcomprises a localization device (19) and localization module (21)configured to provide the processor (26) with three-dimensional spatialcoordinate system positional data, such as X-Y-Z position of the distalportion of an ultrasound transducer (16) within a Cartesian coordinatesystem at the time an image in a sequence is acquired, or X-Y-X positionin addition to orientation data at the time an image in a sequence isacquired, pertinent to the structure to which one or more localizationdevices is coupled, which may be associated with acquired image data toposition and/or orient slices precisely relative to each other andcorrect for relative movement between an ultrasound transducer (16) andsurrounding pertinent structures during an acquisition cycle outside ofthe expected rotational relative movement between the ultrasoundtransducer (16) and surrounding structures. Having position and/ororientation data acquired along with each image in a sequence providesadditional data to the computer which may be utilized to orient thedata, correct the data, and display the data in, for example, intuitivealignment relative to other two-dimensional or three-dimensional imageinformation, as would be apparent to one skilled in the art. In theembodiment depicted in FIG. 4C, a localization device (19) comprisingthree orthogonally-oriented coils is coupled to the distal tip of theinstrument adjacent the transducer (16). An electrical lead (23)positioned adjacent the transducer lead (22) hardware places thelocalization device (19) in communication with the processor (26). Thelocalization device (19) in the depicted embodiment preferably ispartially or fully encapsulated by the distal structure material of theinstrument tip, preferably utilizing a lumen sized to distally house thesmall, three coil localization device (19) construct, and the elongatelead (23) more proximately.

Localization devices (19), such as sets of orthogonally-oriented coilsor other structures, and localization modules (21), generally mounted toa stable structure such as a table and comprising transmitters,receivers, and other components, are available as precise devicelocalization systems from suppliers such as Medtronic Corporation,Ascension Technology Corporation, SuperDimension Ltd., and theBiosense-Webster division of Johnson & Johnson Corporation. Such systemsmay be configured to communicate with a processor (24) via electronicleads (23, 25), as shown in FIG. 4B, and to communicate with each othervia electromagnetic radiation, in a configuration, for example, whereina module comprises an electromagnetic field detector or transmitter, anda device coil comprises a conducting material configured to detectnearby electromagnetic fields. Other conventional localization systemsutilize electrical conductivity or other forms of radiation to detectposition and/or orientation of medical instruments.

Referring to FIG. 4C, further detail of preferred processor (26)componentry is depicted. In the depicted embodiment, the processor (26)comprises a control processor (456) in communication with aservocontroller (452), an image processor (458), and operator controls(454). The image processor (458) is in communication with an ultrasoundmainframe (450) and a display system (28). In one embodiment, thecontrol processor (456) is a conventional personal computer typemicroprocessor resident in a personal computer, and the servocontroller(452) comprises one or more boards for digital and analog signal inputand output also resident in or coupled to the same personal computer,the control processor (456) and servocontroller (452) each beingoperated by software resident on the computer. Many conventional controlsystem software and hardware packages, such as those sold under thetradename “dSPACE” by Digital Signal Processing and Control GmbH ofGermany, are suitable for such an application. The operator controls(454) preferably comprise conventional devices such as a mouse, a footpedal, or a microphone which may be utilized to communicate controlinputs, such as on/off, begin data capture and drive mechanism activity,select a targeted field of view position, etc., to the control processor(456). The ultrasound mainframe (450) preferably comprises aconventional standalone ultrasound device, such as those sold under thetradenames Aspen™, Sequoia™, and Cypress™ by Siemens AG of Germany, andmay be configured to communicate image data to the image processor (458)in one or several modes. For example, in one embodiment, the ultrasoundmainframe (450) receives (22) from the ultrasound transducer (not shownin FIG. 4C) and sends associated image data in video standard format tothe image processor. In another embodiment, the ultrasound mainframesends image data in both video standard format and raw image dataformat.

The term “raw image data” is used in reference to data output from theultrasound mainframe (450) in digital format, generally comprising anarray of ultrasound image strength datapoints within the pertinent fieldof view, each of the datapoints being associated with a polar coordinatereference frame as acquired and then scan converted to rectilinear frameof reference for conventional display visualization. Raw image data maybe sent to the image processor organized in lines, blocks, etc., and incomplete sets as associated with a single image, or a subset, asassociated with a particular portion of an image file, as in thescenario wherein a particular portion of a field of view is of interest.Such data processing and scan conversion to form raw image dataaccessible to a particular display system from a given polar coordinateor rectilinear transducer field of view frame of reference is well knownin the art of ultrasound.

Due to the image capture frequency limitations associate withconventional video standards such as NTSC, 30 frames per second, andPAL, 25 frames per second, it may be desirable to send only raw imagedata for high-frequency updating. In a preferred embodiment, forexample, operator controls, such as a mouse or footpedal, enabletoggling between video standard output format at the frequencyprescribed by the pertinent standard, and output to the image processorat a higher frequency using raw image data, such as at 60, 90, or 120frames per second or other frequencies, for example, depending upon datatransmission and bus considerations between the pertinent components, aswould be apparent to one skilled in the art. In one embodiment, forexample, an operator may use a control (454) such as a mouse to selectfrom an image associated with the entire pertinent field of view aportion of the field of view for high-frequency updating, after whichthe ultrasound mainframe (450) is configured to respond by sending onlythe pertinent lines of raw image data at a higher frequency to the imageprocessor (458). The notion of selecting a subportion of a capturedimage volume is discussed in reference to FIGS. 6A-B and 7A-B.

The image processor may comprise a personal-computer-basedhardware/software system component, or may comprise a standaloneworkstation, such as those sold under the tradename “4-D Cardio-ScanFreehand Workstation” by TomTec Imaging Systems GmbH of Germany.Further, the ultrasound mainframe may be incorporated into apersonal-computer-based hardware/software component. In addition,various components of the processor (26) embodiment depicted in FIG. 4Cmay be incorporated into miniaturized hardware/software components, suchas application specific integrated circuits, field programmable gatearrays, groups thereof, or the like, as would be apparent to one skilledin the art. For example, in one embodiment, both the servocontroller(452) and control processor (456) comprise small integrated circuits incommunication (34) with the drive mechanism (not shown in FIG. 4C) andother components.

Summarizing one preferred functionality of the system embodimentdepicted in FIG. 4B, the processor (26) and associated controls hardwareand software (not shown) is utilized to rotatably drive (302) theultrasound transducer (16) field of view (242) through a selected targetvolume (14) with a rotational pattern sufficient to capture images ofthe targeted objects (224, 10, 12) during resting periods, as monitoredwith the associated biological signal sensor (32). For example, in thecase of monitoring the position of endocardial tissue (10, 12) relativeto a medical instrument (224) positioned in the heart, an EKG-sensingbiological signal sensor (32) may be utilized with the control system toproperly position and reposition the ultrasound transducer (16), or“gate” the ultrasound transducer (16) to the cardiac rest periods, aswould be known to one skilled in the art.

Should the targeted tissue walls (10, 12) comprise the right and leftatrium walls, for example, in a human wherein the average distance fromthe right atrium wall (10) to the far end of the left atrium (12) isabout 10 centimeters, using 50 ultrasound lines and the conventionalultrasound relationship of 13 microseconds per roundtrip centimeter withthe ultrasound transducer (16) positioned centrally, ultrasound imagesmay be sampled at about 154 frames per second, or about 150 Hz perslice. Using this calculated value and a scenario wherein 10rotationally-oriented two-dimensional slices are desired to form arelatively detailed image volume for each acquisition cycle, each imagevolume is acquired at a sampling frequency of about 15 Hz, preferablysubject to pauses for gating around the relatively high-motion systolicheart cycle periods. Should the targeted tissue walls (10, 12) comprisewalls of the left atrium, distances of 5 centimeters or less may besampled at approximately twice these calculated rates (using 5centimeters per ultrasound line as opposed to 10 centimeters perultrasound line). Further, very high resolution images may be acquired,say 100 lines as opposed to 50, and 40 rotationally-orientedtwo-dimensional slices as opposed to 10, at approximately 1.9 Hz, andthe sampling rate for each slice will still be approximately 77 Hz(frequency=1/time=1/[10 centimeter-deep slice*13×10⁻⁶ round trip speedof sound*100 lines]), which is significantly faster than the 30 Hz rateof the NTSC video standard or the 25 Hz rate of the PAL video standard,and has much higher resolution than presented with these videostandards. The use of raw ultrasound data versus video standards invarious embodiments of the present invention are described in furtherdetail below in reference to FIG. 4C.

In another example wherein a high resolution is preferred and slice datais acquired at a rate of about 60 ultrasound slices per second utilizinga system such as those sold by Siemens Corporation, 30 two-dimensionalslices of a targeted volume may be acquired within 500 milliseconds atthe center of the resting period between healthy human heart cycles (30slices=0.5 seconds*60 slices/second), at various rotational positionsabout the rotational axis of the structure to which the ultrasoundtransducer is coupled. In a preferred embodiment, a rotational drivemechanism such as those available from TomTec Imaging Systems GmgH maybe configured to rotate an ultrasound transducer such as that featuredon the product sold under the tradename AcuNav™ by Siemens Corporationat a rate sufficient to achieve approximately 2 degrees of rotationalangular separation between each of the 30 adjacent slices, providing anoverall image volume rotational field of view spanning approximately 60rotational degrees (60=2 degrees between each slice*30 slices). Such asystem preferably is also configured to return the transducer to astarting point during the remainder of the heart cycle to be ready toacquire 30 more slices at similar rotational positions during asubsequent heart cycle resting period. Embodiments such as thosedescribed in reference to FIGS. 4A-4C are useful for not only examiningtissue structures such as the walls of a heart chamber or distal tips ofmedical devices, but also for examining pathology and related tissuestructure behavior, such as the relationships between infarcted regionsof left ventricular myocardium and chamber dynamics such as injectionfraction.

Referring back to FIGS. 3A and 3B, in one embodiment, the field of viewrepositioning motion (302) may be paused or interrupted duringacquisition of each image, while in another embodiment the repositioningmotion may be continued during acquisition of the images. In a scenariowherein the targeted object volume to be imaged does not completelysurround the ultrasound transducer, it may be preferable to rotate thefield of view from a first position (228) imaging the first portion ofthe targeted object volume through to a fourth position (234) imagingthe last portion of the targeted object volume and then reposition backto the first position (228) by rotating the field of view (242) in areverse direction before the next acquisition cycle. Such a scenario isillustrated in FIG. 3A, wherein the targeted object volume asillustrated surrounds the longitudinal axis of the medical device (220)by about 120 degrees. In another embodiment, the ultrasound transducermay be rotated around in the same direction for 360 degrees with such anangular velocity that it is returned from the last position (234) backto the first position (228) before the start of a successive acquisitioncycle. In another embodiment, the transducer may be rotated (302) at anangular velocity sufficient to facilitate more than one completeacquisition cycle during a single resting period between adjacentsystolic heart cycles. In another embodiment, the transducer may becontinuously rotated (302) throughout a single heart cycle or series ofheart cycles, with blurring of the surrounding structures in imagesacquired during cyclic motion of the heart and slightly bowed or blurredimages in the transition between each resting period and dynamic heartcycle period.

Continuing the analogy to the conventional imaging technique as depictedin FIGS. 2A-2C, FIG. 3B depicts a scenario wherein the improvedtechnique involves four acquisition cycles (250, 252, 254, 256), each ofwhich is positioned within a resting period, and each of which comprisessuccessive image acquisition and repositioning from a first position(228) to a fourth position (234) before repositioning back to the firstposition (228) for the next successive acquisition cycle. Referring toFIG. 3C, the result is an improved ability to visualize and displaythree dimensional relative motion of objects within the targeted volumeover time through compilation of successive image volumes (804, 806),each of which comprises images preferably acquired within the same heartcycle. A comparison (809) of a first image volume (804) comprising fourtwo-dimensional images from a first acquisition cycle (250) to a secondimage volume (806) comprising four two-dimensional images from a secondacquisition cycle (252), and so on for additional acquisition cycles(254, 256, etc), facilitates an improved ability to visualize changes ina displayed image volume due to the fact that the accuracy ofrepresentation of the relative position of objects within each imagevolume is not dependent upon homogeneity of heart cycles or acquisitioncycle gating across many heart cycles. Using this technique, errorsintroduced by gluing many two-dimensional images together into onethree-dimensional image in the presence of other out-of-cycle motion,such as breathing motion in the presence of heart motion, areeliminated, and an observer is provided with images representative ofthe relative positioning of objects, such as medical instruments andtissue masses, versus time. In comparison to the conventional techniquesdescribed in reference to FIGS. 2A-2C, wherein images are glued togetherfrom several moments in time and may be substantially useless forobserving or guiding objects within a body in near real time, theinventive techniques provide three-dimensional relative positioningvisualization based upon series of actually-acquired images, displayedin near real time. The term “near real time” is used in reference to thedisplaying images on a real-time pace but slightly behind actual realtime due to the time associated with acquiring, processing, anddisplaying images using computerized hardware and software. Using asystem with a processor (26) such as that depicted in FIG. 4C, near realtime visualization with a time shift of less than about one second, orabout one heart cycle, may be achieved. As would be apparent to oneskilled in the art, subsequent to acquisition and processing, digitalvideo or images may be controllably displayed at rates faster or slowerthan actual real time, or even in reverse, using conventional signalprocessing techniques. Further, to decrease the pitch of the imageslices comprising a given image volume before displaying aspects of theimage volume, additional intermediate slices may be created and added byinterpolation or averaging values between adjacent actual slices.

Referring to FIGS. 5A and 5B, differences between a conventionaltechnique and an embodiment of the inventive technique are highlightedin flowchart format. As shown in FIG. 5A, a conventional techniqueinvolves moving a transducer field of view to a first position (400),acquiring multiple images at that position during various points in timeduring a resting period (402), then moving the transducer field of viewto a second position (404), acquiring multiple images at that positionduring various points in time during a resting period (406), moving thetransducer field of view to a third position (408), acquiring multipleimages at that position during various points in time during a restingperiod (410), moving the transducer field of view to a fourth position(412), and acquiring multiple images at that position during variouspoints in time during a resting period (414), after which the acquiredimages may be “glued together” as described above in reference to FIGS.2A-2C to facilitate visualization of the relative positions of objectsin the target volume over time.

Referring to FIG. 5B, one embodiment of the inventive techniquecomprises moving a transducer field of view to a first position (420),acquiring a first series of images as the field of view is advanced fromthe first position through to the fourth position (422), then returningthe transducer back to the first position (424) for successive similarcycles (426, 428, 430, 432, 434).

In another embodiment, each image volume may be acquired over two ormove heart cycles. For example, in the case of a relatively large targetobject volume, it may be desirable to acquire a first half or third ofan image volume during a first resting period utilizing theaforementioned technique of repositioning between acquisition of eachimage, followed by a pause in repositioning and acquisition during asystolic heart cycle, and continuation through the second half or thirdof the image volume acquisition during a subsequent resting period, andso on. To reduce errors associated with spreading an image volume acrosstoo many different heart cycles, as discussed above in reference toconventional techniques, it is preferable to acquire the entire imagevolume during adjacent resting periods, and even more preferably in asfew adjacent resting periods as possible. As noted above, repositioningand image acquisition preferably are paused during systolic cyclesbetween resting periods—but in one embodiment, repositioning and imageacquisition may be continued during systolic cycles resulting in someimage artifact that may be removed with conventional image processingtechniques or simply ignored, subject to the aforementioned preferencethat the acquisition of the image volume is continued after the systoliccycle during the next available successive resting period to improveaccuracy.

In one embodiment, for example, a first half of a first image volume isacquired during a first resting period, and a second half of the firstimage volume is acquired in a second resting period to completeacquisition of the first image volume. Then the first half of a secondimage volume is acquired during a third resting period, followed bycompletion of acquisition of the second image volume during a fourthresting period. The first and second completed image volumes may then becompared, as discussed in reference to FIG. 3C, to facilitatevisualization of differences in relative positions of objects within thetargeted object volumes.

In another embodiment, a simplified system such as that depicted in FIG.4A may be utilized to continuously gather images at a given frequency asthe ultrasound transducer (16) is continuously repositioned (302) at asubstantially constant angular velocity without pausing andrepositioning to a given start point. Images acquired during therelatively high activity of systolic heart cycles present as distortionin processed and displayed images, but the relative positioning between,for example, a medical instrument (224) and a tissue wall (10, 12), forguidance and operative purposes is presented accurately in between thedistorted images—with a relatively simple system configuration.

Referring to FIG. 6A, a targeted object volume may contain a significantamount of unneeded data for purposes of observing the relativepositioning between two objects, such as a medical device (224) and atissue wall (222). It may be desirable, therefore, to acquire anddisplay changes in a large image volume, and then also allow a user tofocus updating of the image volume upon a smaller, more concentratedimage volume—preferably one focused upon the object volume regionsclosest (500) to the relative positioning of the two objects of interest(224, 222), as depicted in FIG. 6B. Such “zooming-in” may beaccomplished by “cropping” each image dataset, or limiting the datacomprising each image which is sent to the display system (28). Imagecropping may be complemented or improved by modifying gain andtransducer transmission focus utilizing well known ultrasoundrelationships. For example, if a rotating ultrasound transducer (220) isconfigured to rotate through a field of view of approximately 100degrees, as depicted in FIG. 6B, with a transducer gain and transmitterfocus configured to capture image data from directly adjacent thetransducer (200) to a position well beyond the farthest object ofinterest, there is an opportunity to modify gain and transducertransmission focus for optimized performance with a more concentratedimage volume (500), and also crop the acquired datasets to focus on theconcentrated image volume (500) without updating, compiling, anddisplaying to the full extent of the system as positioned.

FIGS. 7A and 7B depict an illustrative embodiment wherein there is adecreased need to continually acquire compile, and display differenceswithin a larger image volume envelope (600) since a smaller, croppedimage volume envelope (602) provides the requisite data for observingrelative positioning between two objects (222, 224).

A decreased range-of-motion may also be utilized to focus on aparticular aspect of a larger image volume. For example, if afterviewing a larger image volume acquired with about 180 degrees ofrepositioning rotation, it becomes apparent that the key area of focus,due to the position of a pertinent tissue structure or other object, isaround the middle 60 degrees of the larger target volume, then therotation and repositioning of the transducer may be focused totemporarily repeatably acquire data in the middle 60 degrees of thetarget volume. Referring to FIGS. 7C and 7D, embodiments illustrative ofrange of motion zooming-in to form a decreased volume envelope (601). Asshown in FIG. 7C, an embodiment is depicted wherein range of motionzooming-in through a reduced field of view swing angle (603) causesimage acquisition to be focused on a decreased volume envelope (601).FIG. 7D depicts a side view of a similar embodiment wherein a reducedfield of view swing angle (603) focuses image acquisition upon adecreased volume envelope (601). At a given field of view swing angularvelocity at which the transducer swings through the pertinent field ofview, a decreased field of view swing angle (603) such as those depictedin FIGS. 7C and 7D generally contributes to faster cycling of thetransducer through the pertinent field of view. This may be advantageousin scenarios wherein fast updating is preferred. For example, dependingupon system throughput issues such as data bus and swing angularvelocity, it may be difficult to gather data through a large swing anglewith the limited time during a diastolic heart cycle resting period, andthen conduct a repositioning swing to place the transducer in a readyposition before the start of the immediately subsequent diastolic heartcycle resting period—but a reduced field of view swing angle may changethis dynamic significantly, facilitating capture of an entire reducedvolume envelope (601) during each diastolic resting period.

Multiple modalities of focusing or zooming-in upon a smaller imagevolume may be combined. For example, both range-of-motion limitation andimage cropping may be utilized upon to focus upon a particular imagevolume and provide greater image throughput, which may facilitate higherfrequency display updating, depending upon the data bus and processinglimitation of the various components of the system, as would be apparentto one skilled in the art.

For example, in one preferred embodiment, the display system (28) isconfigured to show two images—one of a larger image associated with alarger image volume, and a second of a smaller focused image volume.Utilizing operator controls (454) such as a mouse, the operator mayselect a focus volume from the larger image, the focus volume beinglimited by range-of-motion, cropping, or both, subsequent to which thesecond image associated with the focused image volume is updated atrelatively high frequency due to the data throughput increasesassociated with the smaller image volume. Should the user becomedisoriented or wish to toggle away from the smaller image volume back tothe larger image volume, such a selection may be made with operatorcontrols, such as a mouse, footpedal, or microphone, to return back tothe original image updating frequency for the larger volume, subsequentto which a similar toggling may be utilized return high frequencyupdating to the smaller image volume. Alternatively, the additionalthroughput associated with the smaller image volume may be utilized togather images at a decreased pitch through the selected smaller imagevolume for enhanced image volume resolution. In another embodiment, alarger image volume may be updated at a lower frequency than anassociated smaller focus image volume. For example, in such anembodiment, a first displayed image may represent an image volume“snapshot” of the larger image volume as updated every five or six heartcycles, and a second displayed image may represent a smaller imagevolume as updated one or more times per heart cycle in between thelarger image volume snapshot cycles.

Referring to FIG. 8A, a selected smaller-sized image volume (602) isdepicted encapsulating the relative positioning of a subject tissue mass(222) and a medical instrument (224). In an embodiment wherein fourimages (700, 702, 704, 706) are acquired from the limited image volume(602) during rotational repositioning (302) of the depicted side-firingultrasound catheter (220), the rotational positioning (228, 230, 232,234) of the images (700, 702, 704, 706) relative to the position of theultrasound catheter (220) may be as depicted in FIG. 8B. As describedabove, these four images may subsequently be displayed as an imagevolume from the perspective of the ultrasound catheter (222) using theaforementioned techniques.

Alternatively, it may be useful to display the image volume from adifferent perspective in space—i.e., one other than the perspective asacquired from the position of the side-firing ultrasound catheter. Forexample, referring to FIG. 8C, a simulation of a view of one of theimages (704) from FIG. 8B is depicted as viewed from a calculatedperspective approximately 90 degrees orthogonal to the perspective asacquired. As shown in FIG. 8C, a view of the image data from arecalculated perspective, produced utilizing conventional techniquessuch as those employed in computed tomography and magnetic resonanceimaging systems, is displayed in FIG. 8C in a perspective typical ofthose conventionally utilized with two-dimensional ultrasound devices.Depending upon the pertinent dataset underlying the image, such a viewmay be particularly useful for visualizing the relative positioningbetween the subject tissue mass (222) and the medical instrument (224).Indeed, such a perspective may be highly useful for viewing several ofthe four images (700, 702, 704, 706) acquired during an acquisitioncycle such as that depicted in FIGS. 8A and 8B.

Furthermore, a recalculated perspective may be useful for visualizingthe changes in a given image from one acquisition cycle to another. Forexample, FIG. 8D depicts four sets of four images, each set beingacquired during a different acquisition cycle (750, 752, 754, 756), inan analogous fashion to those described above in reference to FIGS.3A-3C. Perspective recalculation may be described in terms of twofactors: perspective origin, and perspective vector. Referring to FIG.8C, for example, the perspective origin, as viewed by the reader of FIG.8C, is at the viewer's eye location above the page, while theperspective vector is from the viewer's eye into the page upon which thedrawing is printed. The notions of perspective origin and perspectivevector are described in further detail below in reference to FIGS. 8Gand 8H. The capability to orient and dissect a three-dimensionalorientation of images to visualize structures of interest in manners notavailable by viewing one of the acquired two-dimensional images can besignificantly advantageous.

In addition to perspective recalculation, image alignment within eachseries or recalculated series may be useful for observing relativepositioning of objects within a given image volume. For example, it maybe preferable to realign or reorient each of the images in a givenseries with or without perspective recalculation. Referring to FIG. 8E,for example, each of the four images (700, 702, 704, 706) naturallyoriented per the acquisition perspective as depicted in FIG. 8B, 8D, or8F has been reoriented to form an image stack (760) having a volumetricshape (762) roughly equivalent to that of a rectangular prism. Thisvolumetric shape (762) may be preferred, for example, in a scenariowherein the observer desires to see if there is any contact between amedical instrument (224) and a tissue mass (222) from a perspectiveorigin (780) and perspective vector (782) as depicted in FIG. 8E.

In one embodiment of the inventive system, perspective origin andperspective vector may be selected by the user using operator controls.For example, in one embodiment, a mouse or other pointing device isutilized by the user to position a dot representing a perspective originlocation superimposed upon an updated image volume, and to drag themouse or pointing device to select the perspective vector associatedwith the particular perspective origin, while a recalculated view of theupdated image volume is displayed adjacently in another display frame inaccordance with the selected perspective origin and vector. Tools andsoftware for recalculating and presenting perspective views based uponselected perspective parameters are well known in the art of imageprocessing, and are commonly featured in software applications such asthe one sold under the tradename “Solidworks™” by SolidworksCorporation.

In another embodiment, perspective origin, perspective vector, and imageorientation may be selected using controls similar to those describedabove, with the addition of image orientation selectability. In oneembodiment, for example, a user is able to selectably toggle between arectangularly stacked orientation, as in the illustration of FIG. 8E,and an oriented as acquired orientation, as in the illustration of FIG.8F, using a graphical user interface, as updated images of an imagevolume in an adjacent viewing window are modified accordingly.

Referring to FIGS. 8G and 8H, four sets of four images are depicted indifferent orientations with various perspective origins and perspectivevectors for illustrative purposes. Referring to FIG. 8G, each of theimages in each of the four series (750, 752, 754, 756) is oriented asacquired about an ultrasound catheter (220). Two different perspectiveorigins (770, 772) are depicted, each with a different perspectivevector (784, 786). One of the depicted perspectives (772, 786)), forexample, effectively places the viewer within the image stack lookinginto the third acquired image in the stack toward the second. With theother depicted perspective (770, 784), the viewer is effectively placedoutside of the image stack looking into the third acquired image towardthe fourth. As would be apparent to one skilled in the art, theselectability of perspective origin and perspective vector gives anoperator innumerable potentially useful views of stacked image data, anyone of which may be the most valued from a relative positioning orguidance perspective, depending upon the structures involved.

Referring to FIG. 8H, four sets (750, 752, 754, 756) of four images aredepicted in an analogous fashion to those of FIG. 8G, with the exceptionthat the images acquired within each acquisition cycle have beenreoriented to a rectangularly stacked orientation similar to thatdescribed in reference to FIG. 8E. Two different perspective origins(776, 778), each with a different perspective vector (788, 790), aredepicted for illustrative purposes. As shown in FIG. 8H, one of theperspectives (776, 788) effectively places the viewer outside of therectangularly-oriented image stack looking diagonally at an orthogonalview of the stack toward the first acquired image of the stack. Theother illustrated perspective (778, 790) effectively places the viewerinside of the image stack looking toward the third acquired imagestraight through second and first acquired images in the stack.

In another embodiment, two related but slightly different perspectivesmay be calculated and presented for a three-dimensional display effect.Referring to FIG. 9A an image stack is depicted with two different butrelated perspectives. Each of the images in the series of FIG. 9A isoriented as acquired about an ultrasound catheter (220). Two convergingperspective vectors (54, 56) and two slightly separated perspectiveorigins (50, 52) are utilized to calculate two perspectives—each ofwhich is presented to a different eye of an operator using conventionalthree-dimensional display techniques. The spacing (58) between theperspectives is representative of the intraocular distance utilized tosimulate three-dimensional perspectives using conventional hardware andtechniques. For example, polarized goggles and image shuttering, colorseparation from one perspective to another and goggles with lenses ofdifferent color, goggles with separate displays to broadcast separateperspectives to separate eyes, “glasses-free” three-dimensionalperspective monitors such as those available under the tradename“SynthaGram™” by StereoGraphics Corporation, or mirroring to direct thetwo eyes to separate displays, each of which broadcasts a separateperspective, such as the imaging systems available from IntuitiveSurgical Corporation, all are conventional three-dimensional viewingmodalities which may be incorporated into an embodiment of the inventivesolution.

Referring to FIG. 9B, an embodiment analogous to that of FIG. 9A isdepicted, with the exception that the image stack has been reorientedinto a rectangularly stacked orientation. As with the embodimentdepicted in FIG. 9A, two converving perspective vectors (64, 66) and twoslightly separated perspective origins (60, 62) are utilized tocalculate two perspectives—each of which is presented to a different eyeof an operator using conventional three-dimensional display techniques.Similarly, the spacing (58) between the perspective origins (60, 62) isrepresentative of the intraocular distance utilized to simulatethree-dimensional perspectives using conventional hardware andtechniques. In a preferred embodiment, one of the operator controlspertains to adjustability of the spacing (58) between perspectives toaccommodate the variability in intraocular spacing among individualoperators.

Although the invention is described herein with reference to specificembodiments, many modifications therein will readily occur to those ofordinary skill in the art. Accordingly, all such variations andmodifications are included within the intended scope of the invention asdefined by the following claims.

1. A method for acquiring two-dimensional ultrasound images of a heartfor display in a three-dimensional orientation, the heart having a heartcycle, the method comprising: locating an instrument in the heart, theinstrument having an axis and carrying a (transducer; acquiring, withthe transducer, a sequence of images during a single heart cycle,wherein each image of the sequence is acquired at a different rotationalorientation of the transducer about the axis; and displaying theacquired images of the sequence as a three-dimensional, volumetricimage.
 2. The method of claim 1, wherein locating an instrument in theheart comprises intravascular delivery of the instrument into the heart.3. The method of claim 1, wherein each image of the sequence is acquiredduring a resting period of the heart cycle.
 4. The method of claim 1,wherein each image of the sequence is acquired at a rotationalorientation differing from that of the previously acquired image by asubstantially constant angular rotation value.
 5. The method of claim 1,wherein the images of the sequence are acquired by rotating thetransducer about an axis with interruptions in rotational movement foracquisition of each image in the sequence.
 6. The method of claim 1,wherein the images of the sequence are acquired by rotating thetransducer about an axis without pauses in rotational movement foracquisition of each image in the sequence.
 7. The method of claim 1,further comprising acquiring transducer spatial position informationalong with each image of the sequence at the time each image isacquired.
 8. The method of claim 1, further comprising acquiringtransducer spatial orientation information along with each image of thesequence at the time each image is acquired.
 9. A method for acquiringtwo-dimensional ultrasound images of a heart for display in athree-dimensional orientation, the heart having a heart cycle, themethod comprising: locating an instrument in the heart, the instrumenthaving an axis and carrying a transducer; acquiring, with thetransducer, a first sequence of images during a first heart cycle,wherein each image of the first sequence is acquired at a differentorientation of the transducer about the axis; acquiring, with thetransducer, a second sequence of images during a second heart cycle,wherein each image of the second sequence is acquired at a differentorientation of the transducer about the axis; displaying the acquiredimages of the first sequence as a three-dimensional, volumetric image;and displaying the acquired images of the second sequence as athree-dimensional, volumetric image.
 10. The method of claim 9, whereinlocating an instrument in the heart comprises intravascular delivery ofthe instrument into the heart.
 11. The method of claim 9, wherein eachimage of the first and second sequences is acquired during a respectiveresting period of the heart cycle.
 12. The method of claim 11, whereinthe images of the first and second sequences are acquired duringrespective resting periods of immediately adjacent heart cycles.
 13. Themethod of claim 9, wherein each image of the first and second sequencesis acquired at a rotational orientation differing from that of thepreviously acquired image in the respective sequence by a substantiallyconstant angular rotation value.
 14. The method of claim 9, furthercomprising acquiring transducer spatial position information along witheach respective image of the first and second sequences.
 15. The methodof claim 9, further comprising acquiring transducer spatial orientationinformation along with each respective image of the first and secondsequences.
 16. The method of claim 14, wherein the transducer spatialposition information is utilized to align the volumetric images of thefirst and second sequences upon a graphical display.
 17. The method ofclaim 15, wherein the transducer spatial orientation information isutilized to align the volumetric images of the first and secondsequences upon a graphical display.
 18. A method for acquiringtwo-dimensional ultrasound images of a heart for display in athree-dimensional orientation, the heart having a heart cycle, themethod comprising: (a) locating an instrument in the heart, theinstrument having an axis and carrying a transducer; (b) acquiring, withthe transducer, a sequence of images during a heart cycle, wherein eachimage of the sequence is acquired at a different orientation of thetransducer about the axis; (c) displaying the acquired images of thesequence as a three-dimensional, volumetric image; and (d) repeatingsteps (b) and (c) over a sequence of heart cycles.
 19. The method ofclaim 18, wherein locating an instrument in the heart comprisesintravascular delivery of the instrument into the heart.
 20. The methodof claim 18, wherein each image of the respective sequences is acquiredduring a resting period of the heart cycle.
 21. The method of claim 18,wherein steps (b) and (c) are repeated over a sequence of immediatelyadjacent heart cycles.
 22. The method of claim 18, wherein each image ofeach sequence is acquired at a rotational orientation differing fromthat of the previously acquired image in the respective sequence by asubstantially constant angular rotation value.
 23. The method of claim18, further comprising acquiring respective transducer spatial positioninformation along with each image of each sequence at the time therespective image is acquired.
 24. The method of claim 18, furthercomprising acquiring respective transducer spatial orientationinformation along with each image of each sequence at the time therespective image is acquired.
 25. The method of claim 23, wherein thetransducer spatial position information is utilized to align thesequential volumetric images as they are displayed.
 26. The method ofclaim 24, wherein the transducer spatial orientation information isutilized to align the sequential volumetric images as they aredisplayed.
 27. A system for acquiring two-dimensional ultrasound imagesof a heart and displaying the acquired images in a three-dimensionalorientation, comprising: a catheter having a longitudinal axis and adistal end portion carrying an ultrasound transducer; a catheterpositioning system adapted for providing controlled movement of thecatheter distal end about the catheter axis when the catheter distal endis located in a heart chamber; an imaging system coupled to thetransducer and configured to obtain two-dimensional ultrasound images ofa heart chamber with the transducer; and a display coupled to theimaging system, wherein the imaging system is configured to (a) acquire,with the transducer, a sequence of images in a heart chamber during acycle of the heart, with each image of the sequence being acquired at adifferent orientation of the transducer about the catheter axis, (b)display on the display portions of the acquired images of the sequenceas a three-dimensional, volumetric image, and (c) repeat (a) and (b)over a sequence of heart cycles.
 28. The system of claim 27, wherein thecatheter positioning system is configured for vascular delivery of thecatheter distal end into the chamber of the heart.
 29. The system ofclaim 27, wherein the imaging system is further configured to acquireeach image of the respective sequences during a resting period of therespective heart cycle.
 30. The system of claim 27, wherein the imagingsystem is further configured to repeat steps (b) and (c) over a sequenceof immediately adjacent heart cycles.
 31. The system of claim 27,wherein the imaging system is further configured to acquire each imageof a respective sequence at a rotational orientation differing from thatof the immediately previously acquired image in the respective sequenceby a substantially constant angular rotation value.
 32. The system ofclaim 27, further comprising a localization device and a localizationmodule which are together configured to provide transducer spatialposition information along with each image of each sequence at the timethe respective image is acquired.
 33. The system of claim 27, furthercomprising a localization device and a localization module which aretogether configured to provide transducer spatial orientationinformation along with each image of each sequence at the time therespective image is acquired.
 34. The system of claim 32, beingconfigured such that the transducer spatial position information isutilized to align the sequential volumetric images as they aredisplayed.
 35. The system of claim 33, being configured such that thetransducer spatial orientation information is utilized to align thesequential volumetric images as they are displayed.
 36. The system ofclaim 32, wherein the localization device comprises at least oneconductive coil, and wherein the localization module comprises at leastone electromagnetic field transmitter.
 37. The system of claim 33,wherein the localization device comprises at least one conductive coil,and wherein the localization module comprises at least oneelectromagnetic field transmitter.